Frost dates for Thermopolis 21wnw, WY
At Thermopolis 21wnw, the median last spring frost (32°F) is May 29 and the median first fall frost is Sep 17, for a typical growing season of 110 days. For a 90% chance that the last frost has passed, wait until Jun 19. Nearby ZIP codes are in USDA hardiness zone 5a.
- May 29Last spring frost (median)50% chance of 32°F after this date
- Jun 19Safer planting date10% chance of 32°F after this date
- Sep 17First fall frost (median)50% chance of 32°F by this date
- 110 daysGrowing season (median)between 32°F freezes
Last spring frost dates
The chance that the temperature drops to the threshold after each date.
| Temperature | 90% chance later | 50% chance later | 10% chance later |
|---|---|---|---|
| 36°F | May 30 | Jun 17 | Jul 4 |
| 32°F | May 14 | May 29 | Jun 19 |
| 28°F | May 2 | May 14 | Jun 2 |
| 24°F | Apr 17 | May 3 | May 21 |
First fall frost dates
The chance that the temperature has dropped to the threshold by each date.
| Temperature | 10% chance by | 50% chance by | 90% chance by |
|---|---|---|---|
| 36°F | Aug 24 | Sep 6 | Sep 21 |
| 32°F | Sep 3 | Sep 17 | Oct 1 |
| 28°F | Sep 14 | Sep 29 | Oct 10 |
| 24°F | Sep 23 | Oct 6 | Oct 20 |
Growing season length
Days between the last spring and first fall freeze, as the length reached in 9, 5 and 1 out of 10 years.
| Temperature | 9 in 10 years at least | 5 in 10 years at least | 1 in 10 years at least |
|---|---|---|---|
| 36°F | 55 days | 82 days | 104 days |
| 32°F | 87 days | 110 days | 130 days |
| 28°F | 111 days | 134 days | 155 days |
| 24°F | 133 days | 155 days | 175 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 82443 | 5a | -20 to -15°F | 18 km |
Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.
About this station
- NOAA station ID USC00488888, at 43.7231, -108.6964, elevation 1679 m (5,510 ft).
- Data quality: Representative (10+ years), 17 years of freeze data.
- Average days per year at or below 32°F: 207.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Thermopolis (40 km)
- Sunshine 3ne (44 km)
- Thermopolis 9ne (45 km)
- Pavillion (53 km)
- Boysen Dam (56 km)
- Diversion Dam (57 km)
- Burris (61 km)
- Worland (66 km)
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), file dated June 27, 2023; documentation.
- USDA Agricultural Research Service and PRISM Group, Oregon State University, 2023 Plant Hardiness Zone Map ZIP code tables (CONUS, Alaska, Hawaii, Puerto Rico), files dated November 17, 2023. Data © PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed November 1, 2026. Official map: planthardiness.ars.usda.gov.
- U.S. Census Bureau, 2024 Gazetteer ZIP Code Tabulation Areas file, dated August 30, 2024 (ZIP centroids used to find the nearest station).
Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.